Polymer membranes, including nanofiber and microfiber nonwovens are known in the art and are used for a variety of purposes, including in connection with filtration media and apparel. Known techniques for forming finely porous polymer structures include xerogel and aerogel membrane formation, electrospinning, melt-blowing, as well as centrifugal-spinning with a rotating spinneret, and two-phase polymer extrusion through a thin channel using a propellant gas. These techniques are either expensive or do not form nanofibers, e.g., polyamide nanofibers, with acceptable fiber diameter distributions. Electrospinning, in particular, is a relatively expensive process, and current melt-blowing techniques, while less expensive, are unable attain the nanofiber size that electrospinning can attain.
As one example, US Pub. No. 2014/0097558 A1 relates generally to methods of manufacture of a filtration media, such as a personal protection equipment mask or respirator, which incorporates an electrospinning process to form nanofibers onto a convex mold, which may, for example, be in the shape of a human face. US Pub. No. 2015/0145175 A1 provides similar disclosure.
WO 2014/074818 A2 discloses nanofibrous meshes and xerogels used for selectively filtering target compounds or elements from a liquid. Also described are methods for forming nanofibrous meshes and xerogels, methods for treating a liquid using nanofibrous meshes and xerogels, and methods for analyzing a target compound or element using nanofibrous meshes and xerogels. The nanofibers are comprised of polysiloxanes.
WO 2015/003170 A2 relates to nonwoven textiles consisting of webs of superfine fibers, e.g., fibers with diameters in nanoscale or micron scale ranges, for use in articles that have, for example a predetermined degree of waterproofness with breathability, or windproofness with breathability. The fibers may comprise polyurethane-based material or polytetrafluoroethylene.
WO 2015/153477 A1 relates to a fiber construct suitable for use as a fill material for insulation or padding, comprising: a primary fiber structure comprising a predetermined length of fiber; a secondary fiber structure, the secondary fiber structure comprising a plurality of relatively short loops spaced along a length of the primary fiber. Among the techniques enumerated for forming the fiber structures include electrospinning, melt-blowing, melt-spinning and centrifugal-spinning. The products are reported to mimic goose-down, with fill power in the range of 550 to 900.
Despite the variety of techniques and materials proposed, conventional products have much to be desired in terms of manufacturing costs, processability, and product properties.